1. Field of the Invention
The invention is in the field of integrated optics. More particularly it refers to a digital optical switch based on the mode-selectivity principle.
2. Prior art
A digital electro-optical switch is disclosed by references [1] and [2] (see below). The switching action is obtained in said known switch with the aid of so-called mode selectivity. Mode selectivity is the phenomenon that a light mode which is propagated in an optical wave guide, from a point where more than one mode can be propagated, only that mode is excited and propagated whose propagation velocity is best suited to the propagation velocity of said light mode. To be able to generate only one particular mode simultaneously in the switch, a certain asymmetry is required at the input. This known digital electro-optical switch, which is produced on a lithium niobate substrate, possesses said asymmetry in two optical wave guiding input channels of different width, while the output is formed by two optical wave guiding output channels of identical width. The input channels converge at an angle, which has to be less than 0.1.degree., up to a point within their interaction region, while the output channels diverge again at the same angle up to a point outside their interaction region. As a result of a switching voltage applied over electrodes placed in the vicinity of said interaction region and the output channels, the light propagation therein can be influenced electro-optically, in this case, can be switched. This implies that each mode generated in the interaction region can be guided to one of two outputs. A good switching action which is sufficiently polarisation- and wavelength-independent and has a low crosstalk can indeed thereby be obtained. However, a disadvantage is that said digital switch takes up a fairly large space as a component in a matrix of switches owing to its relatively large length as a consequence of the very acute angle (.ltoreq.0.1.degree.) between the straight input channels. Said acute angle also imposes high requirements on the lithography during the production of the component.